ar X iv : a st ro - p h / 06 03 73 2 v 2 10 A pr 2 00 6 Velocity dispersion , mass and the luminosity function of the fossil cluster RX J 1416 .

We study the properties of the fossil cluster RX J1416.4+2315 through g’ and i’-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s−1. Superimposed onto one quadrant of the cluster field there is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km/s. The central object of RX J1416.4+2315 is a normal elliptical galaxy, with no cD envelope. The luminosity function of the system, estimated by the number counts, and statistical background correction, in the range – 22.6 < Mg′ < –16.6, is well fitted by a Schechter function with Mg′ = −21.2 ± 0.8 and α = −1.2 ± 0.2 (H0 = 70 km s−1 Mpc−1, ΩM=0.3, ΩΛ=0.7). The luminosity function obtained from the spectroscopically confirmed members in both g′ and i′ bands agrees with the photometric results. The mass of the system, M ∼ 1.9 × 10 h 70 M⊙, its M/L of 445 h70 M⊙/LB⊙ and LX of 11 × 10 43 h 70 ergs s−1 (bolometric) suggest that this system is the second example of known fossil cluster, after RX J1552.2+2013, confirmed in the literature. Subject headings: cosmology: observations – galaxies: clusters: individual: RX J1416.4+2315 – galaxies: elliptical and lenticular, cD – galaxies: evolution – galaxies: luminosity function, mass function – galaxies: kinematics and dynamics